In a Virtual Private Networking (VPN) environment, a business or enterprise connects multiple remote sites, such as Local Area Networks (LANs) or other subnetwork as an integrated virtual entity that provides seamless security and transport such that each user appears local to each other user. In a conventional VPN, subnetworks interconnect via one or more common public access networks operated by a service provider. Such a subnetwork interconnection is typically known as a core network, and includes service providers having a high-speed backbone of routers and trunk lines. Each of the subnetworks and the core network has entry points known as edge routers, through which traffic ingressing and egressing from the network travels. The core network has ingress/egress points handled by nodes known as provider edge (PE) routers, while the subnetworks have ingress/egress points known as customer edge (CE) routers, discussed further in Internet Engineering Task Force (IETF) RFC 2547bis, concerning Virtual Private Networks (VPNs).
An interconnection between the subnetworks of a VPN, therefore, typically includes one or more core networks. Each of the core networks is usually one or many autonomous systems (AS), meaning that it employs and enforces a common routing policy among the nodes (routers) included therein. Accordingly, the nodes of the core networks often employ a protocol operable to provide high-volume transport with path based routing, meaning that the protocol not only specifies a destination (as in TCP/IP), but rather implements an addressing strategy that allows for unique identification of end points, and also allows specification of a particular routing path through the core network. One such protocol is the Multiprotocol Label Switching (MPLS) protocol, defined in Internet Engineering Task Force (IETF) RFC 3031. MPLS is a protocol that combines the label-based forwarding of ATM networks with the packet-based forwarding of IP networks, and builds applications upon this infrastructure.
Traditional MPLS, and more recently Generalized MPLS (G-MPLS) networks as well, extend the suite of IP protocols to expedite the forwarding scheme used by conventional IP routers, particularly through core networks employed by service providers (as opposed to end-user connections or taps). Conventional routers typically employ complex and time-consuming route lookups and address matching schemes to determine the next hop for a received packet, primarily by examining the destination address in the header of the packet. MPLS simplifies this operation by basing the forwarding decision on a simple label, via a so-called Label Switched Router (LSR) mechanism. Therefore, another major feature of MPLS is its ability to place IP traffic on a particular defined path through the network as specified by the label. Such path specification capability is generally not available with conventional IP traffic. In this way, MPLS provides bandwidth guarantees and other differentiated service features for a specific user application (or flow). Current IP-based MPLS networks (IP/MPLS) are emerging for providing advanced services such as bandwidth-based guaranteed service (i.e. Quality of Service, or QOS), priority-based bandwidth allocation, and preemption services.